Of a plant: able to withstand prolonged rainfall.
Late 19th century; earliest use found in Journal of the Royal Microscopical Society. From ombro- + -philous, in sense 1 after German ombrophil.
Of a plant: shade-loving.
1920s; earliest use found in Bulletin of the Torrey Botanical Club. Apparently an alteration of umbriphilous after ombro- or ombrophilous.